Soybean Plants Modify Metal Oxide Nanoparticle Effects on Soil Bacterial Communities GeYuan PriesterJohn H. C. Van De WerfhorstLaurie WalkerSharon L. NisbetRoger M. AnYoun-Joo SchimelJoshua P. Gardea-TorresdeyJorge L. HoldenPatricia A. 2014 Engineered nanoparticles (ENPs) are entering agricultural soils through land application of nanocontaining biosolids and agrochemicals. The potential adverse effects of ENPs have been studied on food crops and soil bacterial communities separately; however, how ENPs will affect the interacting plant–soil system remains unknown. To address this, we assessed ENP effects on soil microbial communities in soybean-planted, versus unplanted, mesocosms exposed to different doses of nano-CeO<sub>2</sub> (0–1.0 g kg<sup>–1</sup>) or nano-ZnO (0–0.5 g kg<sup>–1</sup>). Nano-CeO<sub>2</sub> did not affect soil bacterial communities in unplanted soils, but 0.1 g kg<sup>–1</sup> nano-CeO<sub>2</sub> altered soil bacterial communities in planted soils, indicating that plants interactively promote nano-CeO<sub>2</sub> effects in soil, possibly due to belowground C shifts since plant growth was impacted. Nano-ZnO at 0.5 g kg<sup>–1</sup> significantly altered soil bacterial communities, increasing some (e.g., <i>Rhizobium</i> and <i>Sphingomonas</i>) but decreasing other (e.g., <i>Ensifer</i>, <i>Rhodospirillaceae</i>, <i>Clostridium</i>, and <i>Azotobacter</i>) operational taxonomic units (OTUs). Fewer OTUs decreased from nano-ZnO exposure in planted (41) versus unplanted (85) soils, suggesting that plants ameliorate nano-ZnO effects. Taken together, plantspotentially through their effects on belowground biogeochemistrycould either promote (i.e., for the 0.1 g kg<sup>–1</sup> nano-CeO<sub>2</sub> treatment) or limit (i.e., for the 0.5 g kg<sup>–1</sup> nano-ZnO treatment) ENP effects on soil bacterial communities.